The present invention relates to a method and apparatus employing a D.C. drive motor and a digital printhead for graphically recording electrocardiographic data on a constant time scale chart record.
It is known to utilize a D.C. drive motor in portable monitoring equipment, such as an electrocardiogram (ECG) so that such portable equipment is of a relatively small size and low weight. There are, however, inherent difficulties with maintaining a constant motor speed and constant time scale when a D.C. motor is employed to drive a strip chart of an ECG. For example, there can be momentary changes in motor speed as a result of change of the load on the motor relating to paper friction or inconsistencies in the paper feed characteristics of the paper roll utilized.
Generally, in prior art portable recorders, the D.C. motor speed may be regulated to maintain a generally constant speed in response to changes on the load of the D.C. motor, but such speed regulation arrangements require additional circuitry which adds to the complexity and expense of such equipment. Typically, such prior art recorders compensate for changes in the load on the D.C. motor to attempt to maintain a constant D.C. motor speed, and data is delivered for recording at a set rate to attempt to provide a constant time scale chart record. The compensation for changes in the load of the D.C. motor are not instantaneous, however, given the mechanical reaction time of the motor and speed regulation arrangements, so that there will be momentary variations in motor speed, which when data is delivered for recording a set rate, results in the recorder failing to provide a uniform constant time scale chart record.
Attention is also directed to the following U.S. patents:
______________________________________ Patentee Patent No. Issue Date ______________________________________ E. G. Fuller, Jr. 4,038,666 07/26/77 Andrews 4,100,470 07/11/78 Patnoi et al 4,214,590 07/29/80 Lowe 4,215,351 07/28/80 Cuvelier 4,417,057 09/09/80 Woods 4,417,254 11/22/83 ______________________________________